Sharpener for cutting instruments



July 25, 1967 J. MCMASTER ETAL 3,332,173

SHARPENER FOR CUTTING INSTRUMENTS Filed June 30, 1964 5 Sheets-Sheet 1 INVENTORS ARCHIE J. M 'MASTER SAMUEL B. M MASTER BY RICHARD K. CARLSON July'25, 1967 J, MOMASTER ETAL 3,332,173

SHARPENER FOR CUTTING INSTRUMENTS Filed June 50, 1964 5 Sheets-Sheet 2 y 1967 A. J. M MASTER ETAL 3,332,173

SHARPENER FOR CUTTING INSTRUMENTS 5 Sheets-Sheet 3 Filed Jun 30 964 United States Patent 3,332,173 SHARPENER FOR CUTTING INSTRUMENTS Archie J. McMaster and Samuel B. McMaster, Deerfield,

and Richard K. Carlson, Chicago, Ill., assignors of onehalf to Cory Corporation, a corporation of Delaware,

and one-half to G-M Laboratories, Inc., a corporation of Illinois Filed June 30, 1964, Ser. No. 379,115 5 Claims. (Cl. 51-128) The present invention relates to a sharpener for cutting instruments, and more particularly, to a sharpener for knife and scissor blades.

Many years ago the cutlery industry established the common practice of grinding knife edges to a 45 included angle. With the early steels, a knife edge that was ground to a substantially smaller included angle than 45 was found to be impractical because the edge would quickly deteriorate in use. Although the steels that are used in almost all knives today are far superior to the earlier steels, the custom of grinding knife edges to a 45 included angle has prevailed. With the development of the motor-driven knife sharpener, such as illustrated and described in U.S. Patent No. 2,775,075 issued to A. J. Mc- Master, et al., the blade guides were positioned so that the customary 45 included angle would be renewed on knife blades when they Were resharpened. Thus, it is common practice at the present time to not only manufacture and sell knives with a 45 included angle blade edge, but to provide sharpeners which will resharpen the knife blades to the same approximate 45 included angle. We have discovered that by grinding the blade edges of recently manufactured steel knives to a 28 included angle, a much greater relative sharpness can be obtained than when the same knives have their edges ground to a 45 included angle.

Therefore, it is an object of the present invention to provide a new and improved sharpener for cutting instruments.

Another object is to provide a motor driven sharpener which will grind the edge of cutting instruments to an approximate 28" included angle.

A further object is to provide a motor driven sharpener which includes two grinding wheels, one of which will grind a blade edge to an approximate 28 included angle, and the other of which can subsequently be utilized to grind a slightly larger included angle on the cutting edge.

A further object is to provide a motor driven sharpener which includes a coarse grit size grinding surface and a second wheel having a fine grit size grinding surface.

Still another object is to provide a motor driven sharpener which is capable of rapidly grinding a coarse 28 included angle on the edge of a cutting instrument blade and of subsequently grinding a smooth slightly greater than 28 included angle on the same cutting edge.

Yet another object is to provide a motor driven sharp ener in accordance with the aforementioned object which also is capable of grinding a smooth cutting edge on a scissors blade.

A specific object of the present invention is to provide a motor driven sharpener having a base through which a coarse grit size grinding wheel and a fine grit size grinding wheel protrude and which has formed therein a guide means for longitudinally moving a scissors blade in contact with a surface of the fine grit size wheel and having a removably mounted structure which, when mounted on the housing, covers the scissors guide means and has formed therein a pair of guide means for grinding an approximate 28 included angle on a knife blade by drawing it longitudinally across surfaces on the coarse grit size Wheel and subsequently grinding a slightly larger than a 28 included angle on the same knife blade by drawing it across surfaces on the fine grit size grinding wheel.

An additional object is to provide a motor driven sharpener which is capable of grinding a predetermined included angle on the edge of a cutting instrument blade regardless of slight axial misalignment between a grinding wheel and cooperating guides.

Further objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of an embodiment of the present invention;

FIG. 2 is a perspective view of the embodiment of the invention illustrated in FIG. 1, with a removable blade guide structure removed from its mounting position on a housing;

FIG. 3 is a perspective View of a portion of the embodiment of the invention illustrated in FIGS. 1 and 2, with the housing removed from a base to reveal an internal mechanism;

FIG. 4 is a top view of the removable blade guide structure portion of the embodiment illustrated in FIGS. 1 and FIG. 5 is a back elevational view of the removable blade guide structure illustrated in FIGS. 1, 2 and 4;

FIG. 6 is a partial front elevational view of the embodiment illustrated in FIGS. 1-5 with a broken away crosssectional view taken along the line 6-6 in FIG. 4;

FIG. 7 is an enlarged sectional view taken along the line 7--7 in FIG. 4 with a blade inserted against the guide and in contact with the grinding wheel;

FIG. 8 is an enlarged sectional view taken along the line 8-8 in FIG. 4 with a blade inserted against the guide and in contact with the grinding wheel;

FIG. 9 is a top elevational view of a portion of the embodiment of the invention illustrated in FIGS. 1-3 with the housing removed and a scissors blade being drawn longitudinally across a grinding wheel; and

FIG. 10 is a cross-sectional view of a knife blade after it is ground by the embodiment of the invention illustrated in FIGS. 1-9.

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will be herein described in detail an embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of principles of the invention, and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

It has been discovered that by grinding steel blades to a 45 included angle, that a relative sharpness value of approximately three is obtained. However, if the same steel blades are ground to a 28 included angle edge, a relative sharpness of approximately 20 is obtained. The present invention makes it possible to purchase ordinary 45 included angle cutting edge knife blades on the Open market and to sharpen them to a 28 included angle edge to provide a much sharper knife than could previously be purchased. Further, the present invention provides a sharpener which will quickly return a knife blade to the increased sharpness provided by an approximate 28 included angle after it has once been sharpened in accordance with the present invention.

The present invention not only makes it possible to increase substantially the sharpness of knives presently sold on the market by decreasing the approximate 45 included angle edge to an approximate 28 included angle edge, but it also provides a method for accomplishing the additional sharpness with a relatively few draws of the blades across grinding wheels by first coarse grinding a blade down to an approximate included angle by a fast cutting coarse grit size grinding wheel and then finishing to a smooth surface by use of a fine grit size grinding wheel. In order that it is not necessary to smoothly grind with a fine grit size grinding wheel, the entire edge which has been prepared by the rough fast cutting grinding wheel, the fine grit wheel places a slightly greater included angle on the cutting edge.

Referring now to the FIGS. 1, 2 and 3, a base plate has an electrical constant speed induction motor 11 mounted thereon so that a driven output shaft 12 of the motor extends out-ward over the base 10. As is more fully described in US. Patent 2,775,075, the motor 11 will stall during a sharpening operation prior to removal of metal at a rate that will burn or otherwise injure a knife blade. A 60 grit size grinding wheel 15 and a 100' grit size grinding wheel 16 are rigidly secured to the shaft 12 in order that they may be rotated by the motor 11. The grinding wheels protrude through respective apertures 17 and 18 of a housing 19 which is normally secured to the base 10 by a set of screws. The 60 grit size grinding wheel 15 has a pair of bevel coarse grinding surfaces 20 and 21, as is more clearly illustrated in FIG. 9. In like manner, the 100 grit size grinding wheel 16 has a pair of smooth bevel grinding surfaces 22 and 23. In addition, the 100 grit size wheel 16 has a third slightly bevel grinding surface 24 on its perimeter.

A removably mounted structure 25 has a pair of apertures 26 and 27 through which the respective grinding wheels 15 and 16 protrude when the structure is mounted upon the housing 19 as illustrated in FIG. 1. A recess 28 is formed in the housing 19 to receive a projection 29 (illustrated in FIG. 6) on the removable structure 25 and a notch 30 is formed in the housing 19 to receive another projection 31 on the inside of the removable structure 25 in order to maintain the structure 25 in a predetermined relative position to the grinding wheels when the structure 25 is mounted on the housing 19- as illustrated in FIG. 1. Referring to the FIGS. 4, 5 and 6 in addition to FIGS. 1, 2 and 3, a pair of blade guides 32 and 33 are integrally formed as surfaces in the structure 25 on either side of the wheel 15 and a pair of blade guides 34 and 35 are integrally formed as surfaces of the structure 25 on either side of the wheel 16.

As may best be seen in FIG. 4, the guides 32 and 33 form 7 angles in a horizontal plane with a centerline 36 of the wheel 15 and the guides 34 and 35 form 7 angles in a horizontal plane with a centerline plane 37 of the wheel 16. As most clearly illustrated in FIG. 9, the bevel grinding surfaces 20 and 21, are inclined at 10 angles to the centerline plane 36 of the wheel 15, and the grinding surfaces 22 and 23 are inclined at 10 angles to the centerline plane 37 of the wheel 16. When knife blades are placed against the respective guides 32, 33, 34 and 35, to draw the blades longitudinally in contact with the respective grinding surfaces 20, 21, 22 and 23, they will contact the grinding surfaces along the section shown in elevation in FIG. 6. As seen in this partial sectional elevational view, the guides 32 and 33 are inclined at 9 angles from the centerline plane 36 of the wheel 15 in this vertical plane which is parallel to the shaft 12, and the guides 34 and 35 are inclined at 11 angles with the centerline plane 37 of the wheel 16 in this vertical plane which is parallel to shaft 12.

The resultant angle of grinding surface contact to a blade placed fiush against the various guides 32, 33, 34 and 35 with the respective grinding surfaces, 20', 21, 22 and 23 are more clearly illustrated in FIGS. 7 and 8, respectively.

Referring to FIG. 7, the combination of placing the surface of the blade guide 32 at an angle of 7 to the centerline plane 36 in a horizontal plane, tilting the surface of the blade guide 32 back at an angle of 9 in a vertical plane parallel to the shaft 12, and so placing the guide 32 longitudinally along the shaft 12 relative to the wheel 15 that a blade laid against guide 32 would contact the grinding wheel 15 at an area which is approximately on a 45 radial of the shaft 12 from a vertical plane passing through the shaft 12 results in a 14 angle being formed at this contact area composed of the edge surface 39 and a centerline plane 40 of a blade such as 33. Similarly the combination of placing the surface of the blade guide 33 at an angle of 7 in the horizontal plane to the centerline plane 36, tilting back the surface of the blade guide 33 at an angle of 9 in a vertical plane parallel to the shaft 12 and so placing the blade guide 33 longitudinally along the shaft 12 relative to the wheel 15 that a blade laid against guide 33 would contact the wheel 15 at an area which is approximately on a 45 radial of the shaft 12 from a vertical plane passing through the shaft 12 results in a 14 angle being formed at this contact area composed of the edge surface 41 and the centerline plane 40 of a ;-inch thick blade such as 38. Therefore, as the blade of a cutting instrument, such as a knife, is drawn along the respective guides 32 and 33, a 14 edge surface 39 is ground on one side of the centerline plane 40 and a 14 edge surface 41 is ground on the other side of the centerline plane 40.

Referring again to FIG. 4, as aforementioned, the surfaces of the guides 34 and 35 make respective 7 angles with a centerline plane 37. Thus the guides 32 and 35 are all positioned at an equal angle to the respective centerline plane surfaces 36 and 37 However, referring now to the vertical plane parallel to the shaft 12 along the section illustrated in FIG. 6, the surfaces of the blade guides 34 and 35 make respective 11 angles with the centerline plane 37 instead of 9 angles as is provided in the same plane between the surfaces of the guides 32 and 33 and the centerline plane 36. The positions of the blade guides 34 and 35 longitudinally along the shaft 12 in relation to the centerline plane 37 are such that the area of contact between a blade laid along the respective guides 34 and 35 will form areas of contact with the grinding surfaces 22 and 23 of the blade 38 which are approximately on a 45 radial of the shaft 12 from a vertical plane passing through the shaft 12. The respective angles of 7 and 11 and the longitudinal position of the guides result in a 16 angle between the respective grinding surfaces 22 and 23 and the centerline plane 40 of the blade 38, as is illustrated for the guide 34 and the grinding surface 22 in FIG. 8. Therefore, if the blade 38 is first sharpened by use of the blade guides 32 and 33 against wheel 15 and then is drawn across the guide surface 34 as illustrated in FIG. 8, it will have an additional edge surface 42 ground thereon, because the guide 34 inclines the blade at a 16 angle to the grit bevelled grinding surface 22 at the area of contact between the blade 38 and the surface 22. Surface 42 will be smoothly ground in contrast to the rough ground surfaces 39 and 41. In like manner, drawing the blade 38 across the grinding surface 23 will result ina smoothly ground surface 43 on the blade 38 which makes a 16 angle with the centerline plane 40 of the blade 38.

Referring now particularly to FIGS. 2, 3 and 9, a scissisors blade guide surface 50 is provided as an integral surface of the housing 19. When it is desired to sharpen the blade of a scissors 51, having blades 52 and 53, the scissors are opened as shown in FIG. 9 and one of the blades, such as 52, is longitudinally moved across the bevel perimeter grinding surface 24 of the wheel 16 against the guide 50. After the blade 52 is so sharpened, the same process is carried out to sharpen the blade 53. The guide 50 is placed sufficiently below the axis of shaft 12 that the grinding surface 24 provides the correct scissors blade grinding angle.

A plate 60 forms a continuation of the outer surface of the housing 19 and is pivotally mounted near its upper fiat portion, so that a rear portion 61 can be pivotally depressed a short distance. The portion 61 of the plate 60 rests upon a spring loaded switch actuator 62 which forms a part of the motor 11 for the purpose of energizing it when it is connected through an electrical cable 63 to a source of electrical potential.

The operation of the embodiment of the invention shown in the drawings'will now be described in greater detail. With the structure 25 mounted in its proper position on the housing 19 as shown in FIG. 1, an operator may proceed to take a conventional knife as presently sold on the general market having a 45 included cutting edge angle and grind it to a thinner cutting edge which has a much higher relative sharpness. The operator places his hand upon the plate 60 which depresses the portion 61 slightly and forces the actuator 62 downward to close an electrical switch (not shown) in the motor 11. This action energizes the motor 11 and it rotates the grinding wheels 15 and 16 through the rotation of a shaft 12. Thus, the operators left hand not only serves to hold the sharpener steady during grinding, but it also simultaneously causes the motor 11 to be energized. With the grinding wheels thus rotating, an operator moves a knife blade longitudinally along the guide 32 in contact with the bevel 60 grit size grinding surface 20 and subsequently moves moves the blade longitudinally along the guide 33 in contact with the 60 grit size grinding surface 21 on the wheel 15. Each time each such pass is made, a little more of the blade is ground away until the area of contact between the blade edge forms the rough ground surfaces 39 and 41 as may be best illustrated by FIG. 10. After this reshaping has been completed on the coarse wheel 15, the operator then draws the knife blade across the guide 34, keeping the blade in contact with the grinding surface 22 and across the guide 35, keeping the blade in contact with the grinding surface 23. Since the grinding of the 60 grit size wheel 15 has ground an edge having the rough area contact surfaces 39 and 41 with a 28 included angled therebetween, the passes against the wheel 16, result in the area of contacts 42 and 43, which make a small smoothly ground set Off surfaces .at the end of the rough ground surfaces with a 32 included angle therebetween. Usually one pass of the knife blade longitudinally against each bevel wheel surface 22 and 23 is sufiicient to establish this construction.

If the blade 38 is thinner than of an inch it will contact the grinding wheels at a lower point with the result that the included angle from rough grinding may be reduced to as small as 20 and the included angle resulting from the fine grinding may be reduced to as small as 24. Similarly, as the grinding wheels wear with prolonged utilization, the -inch blade 38 would contact the wheels at lower points which would result in smaller rough and fine ground included angles. These angles could be reduced to approximately 20 and 24 respectively. Those skilled in the art will recognize that a thicker blade would be ground to slightly larger included angles. Thus, with varying width blades and normal wearing of the grinding wheels, the preferred range of rough ground included angles is 28 to 20 and the preferred range of fine ground included angles is from 32 to 24 with the fine ground included angles being always approximately four degrees greater than the rough ground included angles.

The precise angles of the resulting surfaces illustrated in FIG. are illustrative only. Those skilled in the art will recognize that the angle between the surfaces 39 and 41, could be of the order of 18 or 16 degrees, with the angle between the surfaces 42 and 43, only slightly larger. Although the differences of the angles between the pairs of surfaces is illustrated as 4, this may be decreased to less than /2 a degree or enlarged to an angle of greater than 4. Also, the angle ground by the 100 grit size grinding surfaces may be identical with that ground by the 60 grit size grinding surfaces, so that the entire rough ground surface produced by a 60 grit size wheel may be smoothed by a 100 grit size wheel. This will, of course, require more passes across a 100 grit size wheel than is required when a several degree angle difference is utilized between the two grinding wheel operations. Further, those skilled in the art will recognize that in order to do the fast rough grinding, other sizes of relatively rough grit size grinding Wheels may be utilized and other fine grit sizes may be used for the grinding surfaces of the relatively fine or finishing wheel 16. All such aforementioned modifications and deviations are intended to be within the scope of the appended claims.

If the grinding wheels 15 and 16 should be slightly axially misaligned with the respective guides 3235 the rough ground edge surfaces 39 and 41 will not make exactly equal angles with the centerline plane 40. HoW ever, since both grinding wheels are mounted on the same shaft, the angle of the fine ground surface 42 will still make an approximately two degree greater angle with the centerline 40 than does the surface 39. In like manner, the finely ground surface 43 will still be positioned at a one degree greater angle with the centerline 40 than the rough ground surface 41. Therefore, the position of the surfaces 39-43 illustrated in FIG. 10 maybe retained in respect to each other regardless of axial misalignment of the shaft 12 with respect to the guides 3235. Such misalignment only results in the cutting surfaces being very slightly tilted with respect to the centerline 40. This tilt is insignificant in the resulting cutting capabilities of a blade.

Once a knife is ground to a shape as is illustrated in FIG. 10, it may be resharpened by a single pass of the 'blade along each of the guides 32, 33, 34 and 35. Single passes against the rough wheel are normally sufiicient to remove enough metal that a single pass will be required across each grinding surface 22 and 23 of the fine grinding or finishing wheel 16.

When it is desired to use the illustrated embodiment of the invention for sharpening the blade of a scissors, the guide structure 25 is removed as shown in FIGS- 2, 3 and 9, and the blades such as 52 and 53 of a pair of scissors 51 are longitudinally moved across the grinding surface 24 as aforementioned. Thus the illustrated embodiment of the invention is particularly adapted to providing not only sharper edges on general household and kitchen knives, but it also provides for the sharpening of household scissors.

It will be recognized by those skilled in the art that the present invention is particularly applicable to the blade edge forming and sharpening of all types of cutting instrument blades. Therefore, the method of forming a thinner blade edge, as well as the method of forming a blade edge having a rough cut included angle finished by a smoothly ground pair of edge surfaces which have a slightly larger included angle are intended to be with the scope of the appended claims.

We claim:

1. A sharpener for cutting instruments comprising:

a first abrasive wheel having a pair of bevel grinding surfaces,

a second abrasive wheel having a pair of bevel finer grit grinding surfaces and a third grinding surface forming a part of the outer perimeter of said second wheel,

a rotatably mounted shaft means having said abrasive wheels secured thereon for rotation,

motor means connected to said shaft means for rotating said wheels,

a housing through which said wheels protrude, including a blade guide for positioning the edge of a cutting instrument blade as it is moved longitudinally in contact with said second wheel third grinding surface, and

a structure removably mounted on said housing, enclosing said blade guide when so mounted and including,

a first pair of blade guides for alternatively positioning the edge of a cutting instrument blade as it is moved longitudinally in contact with the respective first wheel grinding surfaces at opposing predetermined angles between a centerline plane of the blade and respective contact areas composed of the blade edge and the grinding surfaces, and

a second pair of blade guides for alternatively positioning the edge of a cutting instrument blade as it is moved longitudinally in contact with the respective second wheel finer grit size grinding surfaces at opposing angles, which are greater than the respective predetermined angles, between a centerline plane of the blade and respective contact areas composed of the blade edge and the respective grinding surfaces.

2. A sharpener for cutting blades comprising:

abrasive wheel means having a first, coarse grit grinding surface and a second, fine grit grinding surface, the grit size of said first surface being approximately 60 and the grit size of said second surface being approximately 100;

an electric motor arranged to be stalled by a relatively small preselected retarding torque;

means for rotating said wheel means as an incident of rotation of said motor;

a fine grinding blade guide adjacent said second grinding surface and forming therewith a predetermined angle of approximately 16 for positioning the edge of a cutting blade for guided longitudinal movement in contact with said second grinding surface to grind said blade edge to said predetermined angle as measured from the flat centerline plane of the blade; and

a coarse grinding blade guide adjacent said first grinding surface and forming therewith a preliminary angle which is maintained approximately 2 less than said predetermined angle for positioning said edge of said cutting blade for guided longitudinal movement in contact with said first grinding surface to rough grind said blade edge to said preliminary angle, thereby to cause the area of contact between said blade edge and said fine grinding surface to be less than the area of contact between said blade edge and said coarse grinding surface and permit the minimum force of the blade edge against said fine grinding surface which will produce said retarding torque to stall said motor to be proportionately greater than the minimum force of the blade edge against said coarse grinding surface which will produce said retarling torque to stall said motor.

3. The sharpener of claim 2 wherein said wheel means includes a third grinding surface having a grit size similar to that of said second grinding surface and a third blade guide is provided adjacent said third grinding surface for guided longitudinal movement in contact with said third grinding surface at a third predetermined angle between a centerline plane of the blade and the contacted third grinding surface.

4. The sharpener of claim 3 further including means precluding access to said third blade guide whenever said coarse and fine grinding blade guides are operatively disposed adjacent said first and second guiding surfaces respectively.

S. The sharpener of claim 2 wherein said preliminary angle between the centerline plane of the blade and the contacted first grinding surface is approximately 14".

References Cited UNITED STATES PATENTS 1,092,877 4/1914 Wallace 51-210 2,021,602 11/1935 Jackson 51218 2,114,106 4/1938 Geveke 51116 2,318,764 5/1943 Dorris 51--128 2,433,512 12/1947 Gorn 51128 2,775,575 12/ 1956 McMaster 51102 2,841,926 7/1958 Lebus 51128 2,860,452 11/1958 Lebus 51102 2,898,709 8/1959 Bednarski 51--128 2,924,047 2/1960 Machovec 51102 HAROLD D. WHITEHEAD, Primary Examiner. 

2. A SHARPENER FOR CUTTING BLADES COMPRISING: ABRASIVE WHEEL MEANS HAVING A FIRST, COARSE GRIT GRINDING SURFACE AND A SECOND, FINE GRIT GRINDING SURFACE, THE GRIT SIZE OF SAID FIRST SURFACE BEING APPROXIMATELY 60 AND THE GRIT SIZE OF SAID SECOND SURFACE BEING APPROXIMATELY 100; AN ELECTRIC MOTOR ARRANGED TO BE STALLED BY A RELATIVELY SMALL PRESELECTED RETARDING TORQUE; MEANS FOR ROTATING SAID WHEEL MEANS AS AN INCIDENT OF ROTATION OF SAID MOTOR; A FINE GRINDING BLADE GUIDE ADJACENT SAID SECOND GRINDING SURFACE AND FORMING THEREWITH A PREDETERMINED ANGLE OF APPROXIMATELY 16* FOR POSITIONING THE EDGE OF A CUTTING BLADE FOR GUIDED LONGITUDINAL MOVEMENT IN CONTACT WITH SAID SECOND GRINDING SURFACE TO GRIND SAID BLADE EDGE TO SAID PREDETERMINED ANGLE AS MEASURED FROM THE FLAT CENTERLINE PLANE OF THE BLADE; AND 